Generation of extreme ultraviolet radiation at 79 nm by sum frequency mixing

High brightness tunable coherent extreme ultraviolet (XUV) radiation at 79 nm with a peak power of ∼200 mW has been generated in H2gas by sum frequency mixing of two quanta from a high spectral brightness ArF* (193 nm) source with one quantum from a tunable dye laser (∼436 nm). Spectroscopic application of this radiation has been demonstrated by observation of a broad (∼160 cm^-1) autoionizing structure in Ar and narrow (∼2 cm^-1) autoionizing features in D2. An analysis is given which identifies the dominant molecular states involved in the nonlinear susceptibility of the medium (H2). The frequency independent tuning behavior of the 79 nm output power observed over ∼300 cm^-1is related to the molecular structure and response of the nonlinear medium in the intense optical field.